The present invention relates to an electric sewing machine with computerized control and more particularly to a machine in which the speed of rotation of at least some moving parts is dependent on the action of an electronic regulator of which the detecting circuit comprises at least one tacho-generator which is kinematically integral with said moving parts and is intended to emit a voltage which is representative of their instantaneous speed of rotation, and at least one source of reference voltage of which the value varies with the position occupied at each moment by a machine actuator, this regulator acting on the speed of rotation of the moving parts by permanent comparison between said voltages.
Numerous sewing machines of this type generally belonging to two distinct categories are already known, that is to say those in which said moving parts are capable of being attached mechanically by the regulator either to a driving motor rotating at a substantially constant speed or to a braking device, depending on whether the signal emitted by the generator moves away from the reference voltage value in one direction or the other, and those in which the moving parts in question are always kinematically integral with a driving motor of the machine, the regulator acting on the current supply of the motor in order to vary the speed of rotation thereof conversely to the deviations observed by the generator relative to the set value fixed by the position occupied by the machine actuator.
The state of the art affected by the first of these two categories of electric sewing machine includes, in particular, Swiss Patent No. 635.382 and U.S. Pat. No. 4,377,778 as well as European Patent Applications published under Nos. 67072, 67649 and 104913.
The second category of electric sewing machines mentioned above is illustrated, for example, in Soviet Patent No. 529.273 and, more recently, by Japanese Kokai No. 57-25187.
As in the case of purely mechanical or electro-mechanical machines, the known electric sewing machines with computerized control all comprise as indispensible accessory a device permitting the user to wind thread onto an empty bobbin, which has on the one hand a rotating support on which the bobbin is detachably fixed and, on the other hand, a driving mechanism for setting this support to rotation.
Such a device can assume different forms and, in particular, like the type shown, for example, in U.S. Pat. Nos. 3,587,494, 4,091,755 or 4,161,153 as well as French Patent No. 2078167, it can comprise a complete clutch system enabling the user instantaneously and kinematically to connect the bobbin support to the electric motor driving the entire machine either directly or via an intermediate moving part driven by it.
The use of an auxiliary low power motor having the sole object of driving the bobbin support directly, which the user can put into service or out of service as desired, has also been proposed (U.S. Pat. Nos. 2,255,152 and 3,741,492, published German Application No. 3501638 A1 and French Patent No. 72.21739).
The disadvantages of either of these two solutions are well known to a person skilled in the art. In fact, although the adoption of a computerized control means should, in principle, enable the number and architecture of parts driven by the machine motor to be substantially reduced, the range of the movements for throwing of the needle and for conveyance of the fabric being imposed "in situ" by individual step-by-step motors driven by the computerized control of the machine, and thus to lead to a structural simplification and, as a corollary, to a reduction in the risks of mechanical breakdown and the production and maintenance costs which should also be translated, in principle, by a reduction in the size of the machine casing and therefore also in its weight, the forced adoption of one or other type of winding device and its inclusion as a "foreign body" among the structural elements used exclusively for the "sewing" operation reduce the impact expected from the adoption of a technical solution which is as sophisticated as that adopted in a sewing machine with computerized control, that is to say in which its different functions are driven by a microprocessor from coded instructions stored in a solid state type read-only memory, in particular a ROM or a PROM.